On December 21, 2023 the Maeslantkering was closed automatically at the 300 cm threshold for the first time in history. During the day a forecast had been made that the water level in Rotterdam would reach critical height of 300 cm above NAP at around 23:30. There were discussions to close the Maeslantkering manually before that time, and the Port of Rotterdam started reducing traffic at 16:00. Around 18:00 the traffic across the Nieuwe Waterweg came to a complete standstill. Before the decision was actually made to manually close the Maeslantkering, the computer systems intervened and had begun the automatic closing procedure. Closing started at 20:15, a process which takes about 2 hours. The next day at 4:45 the gates were opened again.[8]

From the wiki: https://en.m.wikipedia.org/wiki/Maeslantkering

Exactly your first reason, the algorithm is not complex but politics and economics would make it a hard decision for a human.